In terms of air flow, butterfly-type throttles for internal combustion engines are non-linear. For example, when an off-road utility vehicle operates at low throttle, a small change in throttle angle can produce a large power increase. However, when operating near maximum throttle, large changes in throttle angle provide a much smaller power increase. As a result, it is difficult to achieve sensitive low speed control of an off-road utility vehicle.
A non-linear relationship between pedal movement and power output is undesirable for an off-road utility vehicle. Additionally, most power is generated between 0% and about 30% of the accelerator pedal displacement, which may produce between 0 degrees and about 30 degrees of throttle opening angle. As a result, an operator must hold his or her foot at an uncomfortable angle on the accelerator pedal while driving at slow or intermediate speeds.
Variable radius throttle cams have been proposed but have not eliminated the low speed throttle sensitivity problem in off-road utility vehicles. One reason is that there may be insufficient cable displacement between the accelerator pedal and throttle for a cam profile to provide a sufficient difference between low and high throttle behavior.
Additionally, variable throttle controls that include multiple components may be more costly than is acceptable for use on many off-road utility vehicles, and the components may be subject to wear and/or malfunction from normal use. Examples include the devices shown in U.S. Pat. Nos. 4,779,480; 5,239,891; 3,576,140; 5,699,768; 5,078,111; and 4,476,068.
Accordingly, a variable ratio throttle control for an off-road utility vehicle is needed that is low in cost, and that minimizes the number of components that are subject to wear or malfunction. A variable ratio throttle control is needed that can provide a significant difference ratio between low and high throttle openings, with a short throttle cable displacement.